The presently disclosed embodiments are directed to release fluids or agents that are useful in release coating in toner-based technologies. More particularly, the embodiments pertain to the use of hyperbranched polymers with three-dimensional structures in release fluids for an improved contact fusing system to fix toner images to a substrate.
In electrostatographic reproducing apparatuses, including digital, image on image, and contact electrostatic printing apparatuses, a light image of an original to be copied is typically recorded in the form of an electrostatic latent image upon a photosensitive member and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles and pigment particles, or toner. The residual toner image can be either fixed directly upon the photosensitive member or transferred from the member to another support, such as a sheet of plain paper with subsequent fixing or fusing.
In order to fix or fuse the toner material onto a support member permanently by heat, it is usually necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalese and become tacky. This heating action causes the toner to flow to some extent into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to be bonded firmly to the support member.
Typically, the thermoplastic resin particles are fused to the substrate by heating to a temperature of from about 90 degrees Celsius to about 200 degrees Celsius or higher, depending on the softening range of the particular resin used in the toner. It may be undesirable, however, to increase the temperature of the substrate substantially higher than about 250 degrees Celsius because the substrate may discolor or convert into fire at such elevated temperatures, particularly when the substrate is paper.
Several approaches to thermal fusing of electroscopic toner images have been described. These methods include providing the application of substantial heat and pressure concurrently by various means, including fuser members such as a roll pair maintained in pressure contact, a belt member in pressure contact with a roll, a belt member in pressure contact with a heater, and the like. Heat can be applied by heating one or both of the rolls, plate members, belt members, or the like. The fuser member can be in the form of a roller, drum, belt, sheet, film, drelt (a hybrid between a roll and a belt), and the like. The fusing of the toner particles occurs when the proper combination of heat, pressure, and/or contact for the optimum time period are provided. The balancing of these variables to bring about the fusing of the toner particles can be adjusted to suit particular machines or process conditions.
During operation of a fusing system in which heat is applied to cause thermal fusing of the toner particles onto a support, both the toner image and the support are passed through a nip formed between the roll pair, or plate or belt members. The concurrent transfer of heat and the application of pressure in the nip affect the fusing of the toner image onto the support. It is important that minimal or no offset of the toner particles from the support to the fuser member takes place during normal operations. Toner particles that offset onto the fuser member can subsequently transfer to other parts of the machine or onto the support in subsequent copying cycles, increasing the image background, and causing inadequate copy quality, inferior marks on the copy, interference with the material being copied, and toner contamination of other parts of the machine. Such problems, known as “hot offset,” occur when the temperature of the toner is increased to a point where the toner particles liquefy and a splitting of the molten toner takes place with a portion remaining on the fuser member. The hot offset temperature or degradation of the hot offset temperature directly impacts the release properties of the fuser member. Accordingly, it is desirable to provide a fusing surface with low surface energy to provide the necessary release. To ensure and maintain good release properties of the fuser member, release fluids may be applied to the fuser member during the fusing operation to prevent toner offset.
U.S. Pat. No. 4,257,699 to Lentz, the subject matter of which is hereby incorporated by reference in its entirety, discloses a fuser member comprising at least one outer layer of an elastomer containing a metal-containing filler and use of a polymeric release agent.
U.S. Pat. No. 4,264,181 to Lentz et al., the subject matter of which is hereby incorporated by reference in its entirety, discloses a fuser member having an elastomer surface layer containing metal-containing filler therein and use of a polymeric release agent.
U.S. Pat. No. 4,272,179 to Seanor, the subject matter of which is hereby incorporated by reference in its entirety, discloses a fuser member having an elastomer surface with a metal-containing filler therein and use of a mercapto-functional polyorganosiloxane release agent.
U.S. Pat. No. 5,401,570 to Heeks et al., the subject matter of which is hereby incorporated by reference in its entirety, discloses a fuser member comprised of a substrate and a silicone rubber surface layer over the substrate containing a filler component, wherein the filler component is reacted with a silicone hydride release agent.
U.S. Pat. No. 4,515,884 to Field et al., the subject matter of which is hereby incorporated by reference in its entirety, discloses a fuser member having a silicone elastomer-fusing surface, which is coated with a toner release agent, which includes an unblended polydimethyl siloxane.
Different types of release fluids or agents can be used to provide sufficient release. However, the sufficiency of the release depends on the selected release fluid or agent and an appropriate combination of the fuser member surface material and any filler to be incorporated into the fuser member surface material. Despite using appropriate combinations, however, commonly used release fluids or agents, such as those including conventional linear polymers, sometimes still do not provide sufficient release for the toner image.
One approach to the problem is through the use of polymeric release agents having functional groups, either at the chain-end or pendant to the linear chain. The reactivity of functional groups with the surfactants of the fuser member, such as long chain fluorinated acid, helps facilitate robust and uniform incorporation into the release fluid so that rapid wetting of the fluid onto a roller surface is promoted. The use of these polymeric agents, which interact with a fuser member to form a thermally stable, renewable self-cleaning layer having good release properties for electroscopic thermoplastic resin toners, is described in U.S. Pat. Nos. 4,029,827; 4,101,686; and 4,185,140, the disclosures each of which are incorporated by reference herein in their entirety. Disclosed in U.S. Pat. No. 4,029,827 is the use of polyorganosiloxanes having mercapto functionality as release agents. U.S. Pat. Nos. 4,101,686 and 4,185,140 are directed to polymeric release agents having functional groups such as carboxy, hydroxy, epoxy, amino, isocyanate, thioether and mercapto groups as release fluids. U.S. Pat. No. 5,716,747 discloses the use of fluorine-containing silicone fluids for use on fixing rollers with outermost layers of ethylene tetrafluoride perfluoro alkoxyethylene copolymer, polytetrafluoroethylene and polyfluoroethylene-propylene copolymer. U.S. Pat. No. 5,698,320 discloses the use of fluorosilicone polymers for use on fixing rollers with outermost layers of perfluoroalkoxy and tetra-fluoroethylene resins.
However, there are still some problems associated with the use of the above release agents. Common problems include inducement of swelling of fuser member surface coatings, insufficient wetting of fuser members, poor toner adhesion to the support, and poor interaction with the fillers in the fuser members. Additionally, various compositions that have been proposed for treating fuser roll and belt substrates to impart release properties suffer from thermal instability when heated to fusing temperatures, for example, about 150 degrees Celsius and above, for short periods of time of, for example, about 0.5 seconds and longer. Thermal degradation of these release fluids or agents and related derivatives may result in the generation of volatile byproducts.
Thus, while known compositions and processes are suitable for their intended purposes, there remains a need for improved release fluids or agents to help facilitate sufficient release of the fuser member and substantially prevent toner offset. For example, a need remains for release fluids or agents that react well with the surfaces commonly used in fusing systems, without the problems mentioned above, including systems using solid ink jet transfix printing processes.